Such devices have become known in diverse forms of implementation. They are commonly designated by the name of "air bag" and comprise a gas pillow arrangement, whereby a folded bag, mounted on the steering wheel of the vehicle, is suddenly inflated when the ignition of a gas generator is activated by a sensor. Depending on the type of construction this sensor is mounted either on the housing of the gas generator, or within the gas generator, or within the gas pillow arrangement. So far, mostly mechanical or electromechanical sensors have been used.
Through the DE-OS 3,619,937 a safety air bag is known which is integrated with a solid fuel gas generator for forming a preassembled structural unit which includes the sensors and an energy storage device.
These module type units are advantageous in mounting and removal, especially also for retrofitting. They have, however, a series of serious drawbacks. Thus, the gas generator housing requires a special configuration because of the integration and protection of the enclosed or directly connected sensor, which must not be exposed to the generated gas pressure. This leads necessarily to strengthened dimensions for the housing and hence to an increased weight. Furthermore, it has been shown that the reliability is less than optimal because the interface problems permit testing only after final assembly in the vehicle. An additional drawback is that failures in the system always require the exchange of the entire unit.